Improve parsing of template arguments to lay the foundation for

Improve parsing of template arguments to lay the foundation for
handling template template parameters properly. This refactoring:

  - Parses template template arguments as id-expressions, representing
    the result of the parse as a template name (Action::TemplateTy)
    rather than as an expression (lame!).

  - Represents all parsed template arguments via a new parser-specific
    type, ParsedTemplateArgument, which stores the kind of template
    argument (type, non-type, template) along with all of the source
    information about the template argument. This replaces an ad hoc
    set of 3 vectors (one for a void*, which was either a type or an
    expression; one for a bit telling whether the first was a type or
    an expression; and one for a single source location pointing at
    the template argument).

  - Moves TemplateIdAnnotation into the new Parse/Template.h. It never
    belonged in the Basic library anyway.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@86708 91177308-0d34-0410-b5e6-96231b3b80d8